The correct grip size allows you to set the club properly at the top of the backswing. If the grip is too small, it may result in too much hand action and cause the club face to close prematurely, and result in a pull or a hook. Too big and it may cause the clubhead to open up at impact. Find your proper grip size with the virtual Find Your Grip page, or have your teaching professional or club-fitting expert check it for you. Rest assured, Lamkin offers a variety of grips in all grip sizes.
Picking your grip style should be based entirely on feel. Look at Tour pros and you'll see many different styles. It all comes down to personal preference. Choose the grip that gives you the most confidence.
For serious golfers playing regularly, my suggestion is to replace your grips every year. Changing them at the beginning of the season is always a great idea, as you'll have fresh and tacky grips to help maximize control of the clubs right from the outset. Think of it as a tune-up prior to an enjoyable season. In my case, I like the feel of new grips, so I change mine a lot more often than most people.
A good glove works fantastic with the tack of new grips. However, it does not compensate for worn-out grips. You still need good grips, regardless, so that the club won't slip around in your hands during the swing.
I would suggest playing the same style and grip size for woods, hybrids and irons. Most people buy their clubs from different manufacturers, or they buy used clubs. To maintain a consistent feel throughout the set, re-grip all of your clubs with the same grip model and size.
Now, this obviously depends on the condition of your grips. Some golfers haven't changed their grips in five years. You can't tell me that worn grips are giving them the best opportunity to shoot lower scores. I like to minimize my risk of slipping and torque. I need to be confident in my grips. With new grips, my swing is not so tense and I feel more relaxed. I know this produces the best shots, and I believe you'll find that to be true, as well.